1. Transcription
Credit for the original presentation is given to Mrs. Boyd, Westlake High School

2. Choose 3 to discuss with your partner
Conversation Starters
Choose 3 to discuss with your partner
What organelle makes proteins?
What are the monomers of proteins?
What elements make up proteins?
What are the 3 parts of a nucleotide of RNA?
In RNA, adenine base pairs with _________.
Enzyme names have what ending?
Free floating ribosomes make proteins that go where?
Bound ribosomes?
What are ribosomes made out of?

3. I. Review: RNA vs. DNA DNA RNA mRNA, tRNA, rRNA, siRNA… transcription
Key Differences:
ribose sugar
N-bases
uracil instead of thymine
U : A
C : G
single stranded
lots of RNAs
mRNA, tRNA, rRNA, siRNA…
transcription
DNA
RNA

4. A. Central Dogma

5. A. Central Dogma DNA RNA PROTEIN
The CENTRAL DOGMA of molecular biology says that genetic information only goes from DNA in the nucleus to RNA and then to make PROTEINS in the ribosomes.

6. A. Central Dogma - Part 1: DNA RNA PROTEIN Transcription
Genetic information is passed from DNA to RNA by a process called TRANSCRIPTION.

7. B. Overview of Transcription
The process by which genetic information is copied from DNA to mRNA.
mRNA carries genetic information from DNA in the nucleus to the ribosomes in the cytosol.

8. B. Overview of Transcription
RNA polymerase: makes mRNA using one strand of DNA.
coding strand 3 A G C A T C G T 5 A G A A G C A T T T T C T C A A C G
DNA T 3 C G T A A T 5 G G C A U C G U T 3 C
unwinding G T A G C A
rewinding
mRNA
RNA polymerase
template strand
build RNA 53 5

9. Transcription: making a copy
Step 1:
RNA Polymerase unwinds DNA A G C T 3’ 5’
RNA
polymerase T A T A A G C T A T A T 5’ 3’

10. Transcription: making a copy
Exception to base-pair rule: U instead of T!!
Step 2:
RNA Polymerase adds nucleotides to mRNA A G C T 3’ 5’
RNA
polymerase T A T A U C G A A T A T T C G A
mRNA 5’ 3’

11. Transcription: making a copy
Step 3:
mRNA leaves the nucleus and DNA returns to double helix A G C T 3’ 5’ T A T A A G C T U C G A
mRNA A T A T T C G A 5’ 3’

12. C. Transcription Practice (Write it down!)
DNA: ACTGCGTAA
RNA:
DNA: CCTGGATAA

13. QUICK CHECK: Review
What is the enzyme called that makes mRNA from DNA?
What do you call the process of making mRNA from DNA? ____________

14. II. Stages of Transcription
Bacterial chromosome
Transcription
mRNA
Psssst… no nucleus!
Cell
membrane
Cell wall

15. A. Prokaryote vs. Eukaryote genes
1. Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
2. Eukaryotes
DNA in nucleus
linear chromosomes
DNA wound on histone proteins
introns vs. exons
Walter Gilbert hypothesis:
Maybe exons are functional units and introns make it easier for them to recombine, so as to produce new proteins with new properties through new combinations of domains.
Introns give a large area for cutting genes and joining together the pieces without damaging the coding region of the gene…. patching genes together does not have to be so precise.
introns come out!
intron = noncoding (inbetween) sequence
eukaryotic
mRNA
exon = coding (expressed) sequence

16. II. Stages of Transcription
STEP 1: INITIATION
-RNA polymerase starts making mRNA by binding to specific regions of DNA called promoters.
Role of promoter
Starting point
where to start reading
start of gene
Template strand
which strand to read
Direction on DNA
always read DNA 35
build RNA 53

17. II. Stages of Transcription
C: STEP 2: Elongation
RNA polymerase copies DNA as it unwinds
~20 base pairs at a time
bases in gene
builds RNA 53
reads DNA 35

18. II. Transcription in Prokaryotes
D. STEP 3: Termination
RNA polymerase stops at termination sequence

19. III. Transcription in Eukaryotes: Pre-mRNA
The initial mRNA that is made from DNA has segments of introns and exons.
When mRNA has both introns and exons, it is called pre-mRNA.
Introns: sections of pre-mRNA that do not code for amino acids and are not translated into proteins.
Exons: sections of pre-mRNA that code for amino acids and are translated into proteins.
Pre-mRNA

20. While still in the nucleus, the introns that do not code for proteins, are cut out, and the exons are connected. (splicing)
Final mRNA strand made of only exons.
Finished mRNA leaves the nucleus through the nuclear pores.

21. IV. Post-Transcription Processing
mRNA processing (making mature mRNA)
mRNA splicing = edit out introns
add methylated G cap
add polyA tail
3' poly-A tail 3' A A A A A
5' cap
mRNA
A’s P P P 5' G
eukaryotic RNA is about 10% of eukaryotic gene.
intron = noncoding (inbetween) sequence
~10,000 bases
eukaryotic DNA
exon = coding (expressed) sequence
pre-mRNA
primary mRNA
transcript
~1,000 bases
mature mRNA
transcript
spliced mRNA

22. Functions of poly A tail and 5’ Cap
protect mRNA from enzymes in cytoplasm
Helps mRNA leave nucleus
Helps it bind to ribosome

23. QUICK CHECK: Review
Non coding regions of mRNA that are cut out are called _______________
Regions of mRNA that code for proteins are called _________________

24. Looking Forward…
After the mRNA is made from DNA in the nucleus, where does it go?
What are the monomers of proteins called?
What organelle makes proteins?

25. Learning Log: What enzyme is used to make mRNA from DNA?
On what region of DNA does it land to begin transcription? in prokaryotes? In eukaryotes?
Contrast introns and exons.
Why is mRNA necessary for transcription to occur? (why can’t DNA be used)

26. Translation
Credit for the original presentation is given to Mrs. Boyd, Westlake High School

27. Central Dogma

28. Central Dogma - Part 2: DNA RNA PROTEIN
Genetic information is passed from RNA to PROTEINS made by the ribosomes by a process called TRANSLATION.

29. A. Translation Overview
Using mRNA to make a protein by connecting amino acids together.
Occurs at ribosomes outside of the nucleus.

30. Translation: making a protein But why do we need to translate RNA?
The language of DNA and RNA (nucleotides) needs to be translated into the language of proteins (amino acids).
PROTEIN
A,U,G,C
(nucleotides)
Pro, met, ser, val, leu, met…
(amino acids)

31. B. Protein Structure Proteins are made up of monomers of amino acids.
There are 20 different amino acids that can make up a protein.
The sequence of the amino acids determines its shape and function.

32. C. Codons
The genetic information for making proteins encoded in series of three mRNA nucleotides
Codons code for a specific amino acid.

34. QUICK CHECK Codons are found on what type of RNA?
Which nucleotide can vary and still code for the correct amino acid? (1st, 2nd, 3rd)

35. D. Elements of Translation: Start and Stop Codons
The start codon (AUG), which also codes for the amino acid methionine (Met), tells a ribosome to start translating an mRNA molecule.
Stop codons (UAA, UAG, UGA) cause the ribosome to stop translating the mRNA.
An release factor binds to the polypeptide chain and releases it from the ribosome.

37. E. Steps of Translation 1. Step 1:
mRNA leaves the nucleus and goes to the ribosome
Ribosome

38. E. Steps of Translation 2. Step 2:
Ribosome looks for sequence that tells it to start translating = AUG
ribosome
START U C G A

39. E. Steps of Translation 3. Step 3:
Ribosome reads the mRNA strand in triplets called CODONS
ribosome
START U C G A

40. E. Steps of Translation 4. Step 4:
tRNA
leu
E. Steps of Translation
4. Step 4:
RNAs called tRNAs match codons to AMINO ACIDS and transfers it to growing protein.
ribosome
START U C G A

41. QUICK CHECK:
Name the three nucleotide sequence that codes for a start codon on mRNA.
What type of RNA carries amino acids?

42. 4. tRNA and Anticodons Each tRNA molecule binds to 1 amino acid.
Anticodon--a sequence of three nucleotides on tRNA on the end opposite from the amino acid attachment site that pairs with a complementary codon on mRNA

43. QUICK CHECK: Codons are on what kind of RNA?
Anti-codons are on what kind of RNA?
Codon: AUG What is the anti codon?
Codon: UUU What is the anti codon?

44. ribosome
Met
mRNA
Do you know what amino acid comes next?

45. Always use this code with mRNA codons!

46. Met
Ala
mRNA

47. 5. Extending the Polypeptide: Ribosomes
Ribosomes are composed of (2/3) rRNA and proteins.
Ribosomes have three binding sites that are used in translation.

48. 5. Extending the Polypeptide
A site: where incoming tRNA’s with amino acids land.
P site: where amino acids are joined and polypeptide grows.
E site: where tRNA “exits” ribosome and leaves.

49. Embedded or Secreted proteins
All proteins start growing in a free floating ribosome.
Signal peptide: (zip code) tells the ribosome to go to the ER, nucleus, chloroplast, mitochondria
Recognized by SRP RNA: RNA protein complex that directs ribosome to where it needs to go.
Docks to ER
SRP (signal recognition particle)
Protein can be embedded into ER, signal peptide cleaved

50. Learning Log: Where does transcription occur? Translation?
On which type of RNA do you find codons? Anticodons?
Which type of RNA carries amino acids to ribosomes? How many a.acids does each carry?
To use the genetic code (codon dictionary), you look at codons found on what type of RNA?